Kidney Tumor Cells

Kidney tumor cells are abnormal cells that proliferate uncontrollably within the kidney, leading to the formation of a mass or tumor. These tumors can be benign (non-cancerous) or malignant (cancerous). The most common type of malignant kidney tumor is renal cell carcinoma (RCC), which originates in the lining of the renal tubules. Kidney tumor cells are often studied in research to understand the disease biology, find new treatment options, and evaluate the effectiveness of drugs. They can be used to create models such as organoids for these purposes.

Types of Kidney Tumor Cells

RCC, the most common form of kidney cancer, can be further subdivided into clear cell, papillary, and chromophobe subtypes, each exhibiting unique morphological and genetic features. Transitional cell carcinoma, originating from the urothelial lining of the renal pelvis, represents another significant category, while Wilms' tumor, a rare pediatric malignancy, also holds a prominent place in the spectrum of kidney tumor cell types.

• Clear cell RCC. This is the most common subtype of RCC, characterized by the presence of clear, glycogen-rich cytoplasm within the tumor cells. The clear cell phenotype is often associated with alterations in the von Hippel-Lindau (VHL) tumor suppressor gene, a key driver of angiogenesis and metabolic reprogramming in these tumor cells.
• Papillary RCC. It is defined by the presence of papillary or tubulopapillary architectural patterns within the tumor. These tumor cells typically exhibit eosinophilic or basophilic cytoplasm and can be further classified into type 1 and type 2 subtypes based on their morphological and genetic characteristics.
• Chromophobe RCC. It is characterized by its distinctive appearance, with tumor cells exhibiting a pale, reticulated cytoplasm and prominent cell borders. This subtype is often associated with genetic alterations in the TP53 and PTEN tumor suppressor genes.
• Wilms' tumor cells. It also called nephroblastoma, is a rare pediatric malignancy that arises from embryonic kidney cells. These tumor cells are characterized by their undifferentiated, blastemal appearance and can exhibit variable histological patterns, including epithelial, stromal, and blastemal components.

Uncovering Molecular Mechanisms

Kidney tumor cells serve as powerful in vitro models for elucidating the molecular underpinnings of cancer initiation, progression, and metastasis. By leveraging advanced techniques, such as genomic profiling, transcriptomics, and proteomics, researchers have delved deep into the genetic and epigenetic alterations that drive the distinctive phenotypes of these tumor cells.

Preclinical Drug Screening and Development

Kidney tumor cell models have become indispensable tools in the preclinical evaluation of novel drug candidates and therapeutic approaches. By employing advanced in vitro assays, such as cell viability, apoptosis, and migration assays, we can rapidly screen and prioritize drug candidates that selectively target the unique vulnerabilities of kidney tumor cells. Researchers leverage these cellular systems to assess the efficacy, selectivity, and safety of potential therapeutic agents, allowing for the identification of promising lead compounds and the optimization of drug formulations.

Elucidating Tumor Microenvironment Interactions

Kidney tumor cells do not exist in isolation; they are deeply embedded within a complex tumor microenvironment that plays a crucial role in their behavior and therapeutic response. By studying the dynamic interplay between kidney tumor cells and their microenvironment, researchers have gained valuable insights into the mechanisms of immune evasion, angiogenesis, and metastasis.

LZTFL1 Inhibits ccRCC Cell Growth and Proliferation in Vitro and in Vivo

LZTFL1 is a tumor suppressor located in chromosomal region 3p21.3 that is deleted frequently and early in various cancer types including kidney cancer. To investigate the pathophysiological role of LZTFL1 in clear cell RCC (ccRCC), we analyzed LZTFL1 expression in various established ccRCC cell lines. Among eight ccRCC cell lines we tested, LZTFL1 expression is downregulated in ACHN, Caki1, and RCCJF (Fig. 1a). We re-expressed LZTFL1 stably in low-LZTFL1 expressing ACHN and Caik1 cell lines and knocked down LZTFL1 in high-LZTFL1 expressing A498 cell line (Fig. 1b). Proliferation assays by Cell Counting Kit-8 (CCK-8) and colony formation assays revealed that over-expression of LZTFL1 in ACHN and Caki1 cells inhibited cell growth and proliferation capacity. Conversely, the knockdown of LZTFL1 in A498 cells enhanced cell growth and colony formation ability significantly (Fig. 1c, d). Overexpression of LZTFL1 also reduced the size and weight of subcutaneous xenografts in vivo (Fig. 1e). Conversely, knockdown of LZTFL1 promoted the growth of A498 xenograft in vivo (Fig. 1f).

Fig. 1 LZTFL1 suppresses cell proliferation in vitro and in vivo. (Lu J, et al, 2023)

VHLOverexpression Alters Protein Expression Profiling in ccRCC Cells

Quantitative proteomics analysis was conducted on VHL-OE and control cells in biological triplicates for identifying differentially expressed proteins (DEPs). We identified 9459 proteins and 7037 proteins separately with two and more unique peptides quantified. The quantification ratios of biological replicates showed a high correlation, indicating that the results were reproducible (R2 = 0.9) (Fig. 3A). The quantitative ratios were filtered by population statistics to calculate the threshold cut-off as a 50% variation for DEPs. Volcano diagram showed that 404 proteins were up-regulated [VHL-OE/Control > 1.5; false discovery rate (FDR) adjusted P value < 0.05], and 228 proteins were down-regulated (VHL-OE/Control < 0.67; FDR adjusted P value < 0.05) (Fig. 2B). VHL expression was significantly up-regulated, and its substrate HIF1α was significantly down-regulated (Fig. 2B). The expression levels of proteins involved in glycolysis including Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), Triosephosphate isomerase (TPI1), Enolase 2 (ENO2), Pyruvate kinase PKLR (PKLR), and Pyruvate kinase PKM (PKM) were down-regulated in VHL-OE cells compared with those in control cells (Fig. 2C), whereas the expression levels of many subunits involved in the oxidative phosphorylation pathway, including subunits of Complex I, Complex II, Complex III, and Complex IV, were up-regulated in VHL-OE cells (Fig. 2C). The changes of GLUT1, ENO2, and HK2 were validated by RT-PCR (Fig. 2D), while the changes of GAPDH, NDUFV2, and NDUFA4 were further validated by Western blotting (Fig. 2E).

The top 20 pathways enriched by IPA revealed that VHL regulated four major biological processes including metabolism, immune regulation, apoptosis, and cell movement (Fig. 2F). The proteins involved in oxidative phosphorylation, fatty acid oxidation, mitochondrial L-carnitine shuttling, cholesterol biosynthesis, mevalonate pathway, and geranylgeranyl-diphosphate biosynthesis were mostly up-regulated. The number of up-regulated proteins involved in apoptosis and cell movement-related pathways was more than that of the down-regulated proteins (Fig. 2F). Furthermore, we calculated the Z-scores of enriched biological pathways by using the core analysis method in IPA, which assesses the match of observed and predicted up- or down-regulation patterns and represents the non-randomness of directionality within a gene set. The results showed that the apoptotic pathways had Z-scores above 2, suggesting that apoptotic pathways were activated after VHL overexpression. On the other hand, the cell motility-related pathways had Z-scores below −2, suggesting that cell movement-related pathways were inhibited after VHL overexpression. These results indicated that VHL overexpression reduced cell viability and motility.

Proteomics analysis also identified that major histocompatibility antigens HLA-A, HLA-B, HLA-C, HLA-E, and HLA-H were up-regulated in VHL-OE cells (Fig. 2B). The changes were further validated by RT-PCR analysis, showing that the mRNA levels of HLA-A, HLA-B, and HLA-E were also up-regulated (Fig. 2G). This was confirmed by Western blotting, in which both MHC class I molecule HLA-A and MHC class II molecule HLA-DR were up-regulated (3.2-fold and 4.5-fold higher in VHL-OE cells than in control cells, respectively) (Fig. 2H). Intriguingly, PD-L1, an immune checkpoint protein, was down-regulated in VHL-OE cells at both mRNA and protein levels (Fig. 2G and H). Consistently, the gene set enrichment analysis (GSEA) revealed that the expression of antigen processing and presentation signature genes was increased in VHL-OE cells compared with that in control cells (Fig. 2I). These results suggest that VHL overexpression up-regulates both MHC class I and class II molecules, thus enhancing antigen processing and presentation.

Fig. 2 Stable Knockdown of HRP-3 in HCC cells sensitized cells to become shrunk morphology of apoptosis under the energy pressure. (Cai H, et al., 2015)